Method of forming microelements

ABSTRACT

A METHOD OF FORMING MICROELEMENTS OF A GIVEN CONFIGURATION BY PRODUCING IN VACUUM A NUMBER OF SEPARATE ION BEAMS OF MATERIALS, EACH BEAM BEING DIRECTED ONE AT A TIME TO A COMMON PATH. EACH BEAM IS INTENSITY CONTROLLED AND IS ELECTROSTATICALLY FOCUSED ONTO A COMMON WORK PIECE. THE FOCUSED BEAM IS DEFLECTED LATERALLY TO TRACE OUT A TWO-DIMENSIONAL ASPECT OF THE CONFIGURATION OF THEMICROELEMENT, THE IONS BEING DISCHARGED ALONG THE TRACE TO WRITE-IN THE MICROELEMENT, MULTIPLE LAYERS BEING FORMED, IF DESIRED BY DEPOSITNG MATERIAL ON TOP OFPREVIOUSLY DISCHARGED IONS. THE METHOD IS PREFERABLY PERFORMED ELECTRONICALLY IN ACCORDANCE WITH A SEQUENCE OF INSTRUCTIONS DETERMINING THE PARAMETERS FOR A GIVEN TYPE OF MICROELEMENT.

T. HIRSCHFELD METHOD OF FORMING MICROELEMENTS Original Filed April 13,1967 ION.SOURCE,BEAM SELECTIONJNTENSITY. Ei a-aax' w w U CONTROLS 4/5662 9 A [0 9 "20? |O7 H54 98/ 68 94 FOCUS 8 64 CONT PROGRAM 66 CONTROLLED86 DEVICE i f V SCAN 1 90 92 com. l as #7 n6 A 6 I 72 L 7 74 I 4 I02 |O8\4 II V. I06 7 1] a P 5 5:16:55 CONTROL j :14 E us 7' I A I I I i, 84 a285 so 8| United States fatent O i 3,734,769 METHOD OF FORMINGMICROELEMENTS Tomas Hirschfeld, Thousand Oaks, Calif., assignor to BlockEngineering, Inc. Original application Apr. 13, 1967, Ser. No. 630,754.Divided and this application Aug. 6, 1970, Ser.

Int. Cl. B4411 1/18, 1/50 US. Cl. 117-212 8 Claims ABSTRACT OF THEDISCLOSURE A method of forming microelements of a given configuration byproducing in vacuum a number of separate ion beams of materials, eachbeam being directed one at a time to a common path. Each beam isintensity controlled and is electrostatically focussed onto a commonwork piece. The focussed beam is deflected laterally to trace out atwo-dimensional aspect of the configuration of the microelement, theions being discharged along the trace to write-in the microelement,multiple layers being formed, if desired by depositing material on topof previously discharged ions. The method is preferably performedelectronically in accordance with a sequence of instructions determiningthe parameters for a given type of microelement.

This application is a division of copending application Ser. No. 630,754entitled Apparatus for Forming Microelements, filed Apr. 13, 1967, nowUS. Pat. No. 3,547,- 074.

This invention relates to microelements and particu larly to a novelmethod of forming elements of microscopic dimensions.

In the last few decades, devices and techniques for eifectingmicrominiaturization have become increasingly more important. In thefield of optics, ruling engines and photographic methods are employed toprovide even more precise optical devices, such as diffraction gratings,in which the grating period is typically of the order of severalwave-lengths of visible radiation. In electronics, the entire field ofmicrocircuits, including integrated and thin film circuitry, employssuch well-known processes as thermal deposition or epitaxial growththrough masks made by a photographic technique.

Typically, where photographic methods are used to reduce the desiredarrangement of elements to miniature dimensions, several disadvantagesare inherent, for example, the minimum lateral dimensions and themaximum precision of any lateral dimensions are fixed by the wavelengthof light. Devices such as microcircuits formed of several layers, aregenerally produced in a series of separate, independent operationsrequiring considerable production time and frequently a series ofchanged conditions, each diflicult to control. The set-up time forproducing any particular type of circuit is quite long and smallproduction runs or experimental tests of a number of different circuitsbecome quite complex and expensive.

The problems of precision and speed become even more onerous wherepurely mechanical techniques are employed as in ruling of gratings.Clearly, wear and backlash sharply limit the precision obtainable informing microelements mechanically. A fruitless attempt to avoid theseproblems was a broad proposal to form elements with a beam of ions andis described in the paper by W. E. Flynt in ProceedingsThird Symposiumon Electron Beam Technology, Mar. 23-24, 1961, Boston, Mass, R. Bakish,Ed., Alloyd Electronics Corp, pp. 368-379, but no practical approach toimplement the broad concept was provided.

A principal object of the present invention is to provide Patented May22, 1973 apparatus for forming microelements with extremely highprecision and without recourse to photographic or purely mechanicaltechniques.

Other objects of the present invention are to provide a method ofWriting microelements with high accuracy; to provide a microcircuitrydevice wherein a beam of selected ions is focused and selectivelydeflected across a substrate to write-in a deposited microelement on thelatter; to provide apparatus for writing microelements, and comprising asource of ions; means for forming a beam of such ions; means forfocusing the beam to a focal spot; means for controlling intensity ofthe beam to a focal spot; means for controlling intensity of the beam;means for selectively deflecting the focal spot laterally; and means fordischarging the ions at the focal spot so as to effect deposition on asubstrate; to provide apparatus of the type described including aplurality of sources of different ions and means for sequentiallydepositing ions from a said source; to provide apparatus of the typedescribed including means for testing microelements formed by suchdeposition; and to provide apparatus of the type described adapted forautomatic programmed control of selection of ion source, beam intensity,focus, and deflection or any of them.

Generally, these and other objects of the present invention are achievedby apparatus including a hollow sealable elongated enclosure and pumpmeans for maintaining the interior of the enclosure at a considerablyreduced gas pressure, hereinafter generally called a vacuum. Adjacentone end of the enclosure are one or more sources for providing ions ofmaterials that, when discharged, will plate out or deposit on a surface.Means are provided for forming a beam of ions and for focusing the beamto a focal spot. In order to write with the spot thus formed, i.e., tosweep the spot along a predetermined path wherein the ions aredeposited, there is provided means for selectively laterally deflectingthe focused beam. Means are further included for discharging the ionsalong the path or at the target after impact so that their depositiondoes not affect the trajectory of the beam by static buildup. Where morethan one variety of material is to be deposited, means are provided forsequentially controlling the ion sources so that at any given time, theion beam is homogeneous, i.e., is composed of the ions of but a singlematerial.

In a desirable embodiment, means are included for producing anddirecting an electron beam at the deposited material so as to test andevaluate the microelement formed by the ion beam.

Several advantages are to be found in the invention over conventionalmicroforming techniques. For example, not only conductive elements canbe formed, but semiconductors, photoresponsive, capacitive, resistiveand inductive elements can be included. Because the nature of thedeposited or written material, speed of deposition, focal area,direction and speed of beam deflection can all be changed inmicroseconds, completed microelements can be formed in very shortperiods. The entire system, being electrically controlled, allows forprogrammed operation of the process either by direct computerinterfacing or by a programmed memory. With internal test andevaluation, experimental design can be enhanced and improved programsprepared with high speed. The tooling process, for example, to prepare acircuit involves hereby loading the ion sources with appropriatematerials and loading a program into a central unit. Thus, formulationof custom circuitry at reasonable prices becomes feasible.

The accuracy and resolution with which lateral dimensions of amicroelement can be delineated in the present invention, issubstantially increased over the prior art techniques. The ion beams canbe focused to spots as small as 100 A. in diameter if required which,therefore, can be traversed to form lines of similar width; this isquite beyond the capability of thermal deposition techniques.

These and other objects of the invention will in part be obvious andwill in part appear hereinafter. The invention accordingly comprises theapparatus possessing the construction, combination of elements, andarrangement of parts and the several steps and the relation of one ormore of such steps with respect to each of the others all of which areexemplified in the following detailed disclosure and the scope of theapplication of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the presentinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawing wherein:

The drawing is a schematic cross-sectional view, partly in blockdiagram, of apparatus embodying the principles of the present invention.

Referring now to the drawing there is shown a microwriting devicecomprising elongated, hollow, evacuable chamber having disposed thereinadjacent one end, a plurality of ion sources 22, 24, and 26. Typically,the materials to be provided by the latter will include such diversesubstances as metals (e.g. silver, copper, aluminum) gases (e.g.,halogens, oxygen) semiconductors (e.g., germanium, silicon and thelike). Where, for example, the material from which ions are to be formedare gases or can be vaporized at low temperatures, the material can bereadily ionized by electron bombardment in which case the particular ionsource would, as well known in the art, typically comprise a smallenclosure having a leakage -port through which gas, in the interior ofthe enclosure, could pass at a controllable rate as a stream into theinterior of chamber 20. An electron source, typically a heated cathodelocated adjacent the leakage port would provide an electron stream forionizing the gas molecules and suitable electrical fields should besupplied for accelerating the electron stream and for sorting the ionsinto streams of preferred charge. Means (not shown) are preferablyprovided giving access to chamber 20 for loading the ion sources withappropriate materials.

Where the materials to be ionized are not gaseous or readily vaporizedat low temperatures, high temperature molecular ovens can be used in theion sources. The usual oven includes a refractory crucible similar inmaterial to those used in thermal deposition devices, usuallyelectrically heated. The crucible has an aperture therein through whicha molecular beam can issue from the heated material. While frequently asubstantial proportion of the molecules emerging from the aperture willbe ionized, electron bombardment of the molecular beam is desirable toenhance the percentage of ions formed. Alternatively, electric arcsources can be used to provide ions of normally solid materials.

Typically, the ion source is one which can produce positive ion beamsfrom a broad range of elements, such as the source sold as Model 910 bythe Physicon Company, Cohasset, Mass, manufactured by Danfysik Jyllinge,Denmark.

In any event the intensity of emission from all of these ion sources isderived from an electrical power source. Ovens are electrically heatedand the emission intensity is a function of vapor pressure, hence oftemperature and ultimately electric current. The emission intensity ofarc sources is also a function of electrical current, as is theintensity of the electron beam producing the ionization. Thus,electrical control leads 30, 32, and 34 are respectively connected tosources 22, 24, and 26 to provide power to the latter.

While the emission intensity from each ion source can be controlled byregulation of its power supply, in order to achieve high-speed controlthere are provided adjacent @ach ion source, gating mea s f0;Controlling the intensity of the ion streams emitted from each ionsource. To this end, across the path of ion emission from sources 22,24, and 26 are provided respective mesh electrodes 36, 38 and 40.Appropriate bias potentials can be placed on any of the mesh electrodesthrough corresponding electrical leads 42, 44, and 46. Preferably, theion sources are spatially located or arranged so that ion streamstherefrom are substantially parallel to one another.

Alternatively, one can employ a divergence system in which platesinstead of grids are used. In such case, the control potential appliedto the plates should bar the ions or deflect the ion beam so that thelatter impinges on the wall of chamber 20. This is an on-off type ofcontrol as distinguished from a continuous type of control obtainablewith a grid.

Now it will be appreciated that when an ion stream passes through amagnetic or electrical field it will be deflected. If the field ismagnetic, the deflection varies with particle charge, mass, andvelocity; if the field is electrostatic, the deflection varies with thecharge on the ion, its sign, and the ion energy. There is thus providedmeans for deflecting any ion stream from any source to a single commonpath. This is accomplished by disposing a magnetic field source, such aspole pieces 48 (one shown), and an electrostatic field source, such asplates 50, so that their fields are substantially orthogonal to oneanother and perpendicular to the path of the ion streams from sources22, 24, and 26. With appropriate selection of field intensities andcareful placement of the ion sources according to the material to beionized therein an ion stream from any of the sources will be directedby the crossed fields into a single common path without any furtheradjustment of the fields. It will be appreciated that if substantiallyall of the ions coming from the sources are of the same velocity,crossed fields are not necessary. If variation in ion velocity isdesired, it can be achieved after the beams have been channelled to asingle path, by using a variable additional acceleration. Alternatively,the fields can be so chosen as to improve the uniformity of the ionenergy, by allowing only the fraction within a certain velocity to bedirected towards the exit.

This permits one to rapidly change sources as by biasing of meshelectrodes 36, 38 and 40 to full open or to cut-off, yet permitting theion stream, regardless of the source chosen, to be directed to the samepath. Thus, chamber 20 as shown is curved to conform to the general pathof ions from the various sources, an exit aperture 52, defining thefinal common path for the ion stream, being provided in chamber 20.

It will be seen that, in essence, the structure and function of chamber20 and field sources '50 and 48 is akin to the well-known massspectrograph in that the same basic principles are involved, althoughthe present structure operates in the reverse to a mass spectrograph.

Aperture S2 is coupled to another elongated, hollow evacuable chamber54. The axis of elongation of chamber 54 lies parallel to the mean pathof ions passing through aperture 52.

Means are provided in chamber 54 adjacent aperture 52 for providing anaccelerating or decelerating field to ions within chamber 20 andtypically comprises mesh 56 connected to the cylindrical Walls ofchamber 54 and isolated, as by insulation 57, from those of chamber 20.A potential of appropriate polarity derived through lead 58 can beimpressed on mesh 56 creating a constant field region within which othercomponents are disposed. Of course, mesh 56 is disposed to notsubstantially obstruct the passage of ions into and through chamber 54.

Disposed in chamber 54, typically adjacent aperture 52, are means suchas control grid 60, positioned to intercept the path of the ion stream,for providing fine control of the intensity of the ion stream. Grid 60is connectable to a potential source through lead 62. Downstream fromgrid 60 are particle lens means such as apertured disks 64 and 66, forvariably focusing the ion stream to a focal point in a beam ofcontrollable crosssectional characteristics. The structural details andoperating parameters of particle lenses are well-known and need not berepeated here. However, such lenses 'should be of the electrostatic typerather than electromagnetic primarily because the focusing ofelectromagnetic lenses cannot be modulated as quickly as anelectrostatic lens can be, and one can deflect or focus ions ofdifferent masses in the same manner with an electrostatic lens but notwith an electromagnetic lens. This last consideration is highlypertinent here, because the microwriter is intended to employsequentially a number of streams of ions of different weight, each ofwhich would require a change in the magnetic field of a lens system tobe focused to the same point. With the electrostatic lens, field changesare not required to maintain focus. Disks 64 and 66 are respectivelyconnected to leads 68 and 70.

Located downstream, past the electrostatic lens means, are beam-scan ordeflection means such as two sets 72 and 74 of plates for providingcontrollable two-dimensional scanning. The positioning of the deflectionmeans is typical, but the deflection means can also be located upstreamof the lens means or even between the elements of the latter. Thus, set72 comprises two approximately parallel, spaced-apart plateselectrically connected to one another as by lead 76 and disposed suchthat the focused ion beam can pass between the plates. Set 74 is similarto set 72 but the plates of set 74 are orthogonal to the plates of set72 in the usual manner. The plates of set 74 are connected in common tolead 78.

Disposed adjacent the focal point of the beam of ions is movable supportmeans such as block 80 which is preferably of a highly heat conductivematerial so as to serve as a heat sink. Block 80 is of electricallyconductive material and is electrically insulated from contact with thewalls of chamber '54 as by insulating layer 81. In order to insuredischarge of ions incident thereat, block 80 is connected to ground orto some fixed potential with respect to the ions. Means may be provided,if desired, for refrigerating or cooling block 80. In order that block80 can be selectively inserted into or removed from the interior ofchamber 54, there is provided an air lock comprising enclosure 82 havingmovable partitions 84 and 85 at opposite ends, the latter partionforming a wall in common with chamber 54. Appropriate means (not shown)are preferably provided for pumping down enclosure 82.

Connected to leads 68 and 72 is means, shown in block form at 86, forcontrolling the focus provided by disks 64 and 66, by variation of theelectrical potential applied to the latter. Such focal control means arewell known in the art, such as in electron microscopes, so need not befurther detailed here. In similar manner, the deflection plates of sets72 and 74 are connected by leads 76 and 78 to deflection or scan controlmeans shown in block form at 88. The latter also is well known in theart, particularly in connection with cathode ray devices. While both thescan control means and focus control means can be individually andmanually adjustable, it is preferred that their operation be subject toautomatic control. Hence, program controlled device 90 is provided andconnected with both the scan control means, as by lead 92, and the focuscontrol means, as by lead 94, so as to adjust focus, scan or both inaccordance with a predetermined program.

Device 90 can simply comprise an information storage readout system,such as a magnetic tape reader and a group of known analog controls,responsive to the information on a magnetic tape, typically forproviding signals to means 86 and 88 respectively to govern themagnitudes of the potentials provided by the latter to the respectivefocusing elements 64, 66 or/ and the deflection plate sets 72 and 74.Alternatively, device 90 can be an interface with a computer so that theinformation governing operation of the microwriter is derived directlyfrom computation rather than from a storage medium. Device 90 is alsointended to provide signals governing the other functions of elements ofthe microwriter such-as ion activation, ion stream selection, fineintensity control and accelerating voltage. In order to simplify thediscription, a single control means is shown at 96 for controlling thesefunctions as by being connected through leads 30, 32, and 34respectively to ion-sources 22, 24, and 26 by leads 42, 44, and 46respectively to electrodes 36, 38, and 40 by lead 58 to plates 56, andby lead 62 to grid 60. Hence, control means 96 is in turn under thecontrol of program controlled device 90, being connected to the latterby multiple lead cable 98, over the leads of which, the particularsignals can be transmitted to control each respective operation.

Chamber 54 includes an exhaust outlet or port 108 to which is coupledpump 102 for reducing the gas pressure inside chambers 54 and 20, i.e.,evacuating them. Shown schematically is element 104 for reducing spacecharge effects due to the discharge of the ion stream upon discharge ofthe latter. Hence, element 104 is preferably located adjacent block 80.Element 104 is one of a number of different devices capable ofpreventing static buildup at block 88 by rendering conductive the verylow pressure residual gases adjacent block 80. Typically, element 104 isa small microwave antenna intended to have sufficient microwave powerapplied thereto as to ionize the residual gases. Such ionization shouldbe limited to gases as near to the surface of block as possible in orderto prevent the trajectory of the ion beam from being affected. Thus,element 184 is connected by lead 186 to a source 188 of microwave powerwhich is preferably adjustable. Alternatively, of course, element 104can be a gamma or beta ray source, an electron gun providing a largeaperture electron beam for directly discharging the target, or the like.

Lastly, in one embodiment of the invention, positioned adjacent the ionsources, such as 22, is electron scanning beam source 110, typically anelectron gun with beam deflection mechanisms. The latter is connected bylead 112 to control means 96 so that the intensity of the electron beamand its position can be controlled by the latter. Positioned adjacentblock 80 is electron collector means 114 which is connected via lead 116to feed back signals received by collector 114 into programmedcontrolled device 90.

In a typical mode of operation, ion sources 22, 24, and 26 are eachloaded with a different one of the desired materials, and positionedaccording to the nature of the materials so that an ion stream from anyof the ion sources will ultimately be deflected by the fields of thereversed mass spectrograph to a common path through aperture 52. A chipof substrate material 118 is inserted through air-lock 82 and emplacedon block 80. Preferably, chip 118 is bonded to block 80 with a lowmelting point solder so that there can be optimum heat transfer from thechip to the block. The chip itself can be a number of materials,preferably of high heat conductively. Thus, where it is desired to use adielectric substrate, the latter can typically be beryllia, alumina, orthe like both of which are excellent heat conductive materials.Alternatively, the substrate can be an electrically conductive materialmost of which are good thermal conductors and the selection thereof is amatter of choice. If the microwriter is to be used to form asemiconductor circuit, the chip can be germanium, silicon or the like.

Chambers 54 and 20 are then sealed and pump 102 is operated until thetwo chambers are evacuated, typically to a pressure of about l 10' mm.Hg. Ion sources 22, 24, and 26 are then operated to produce ion streams,only one of which at a given instant is allowed to traverse the magneticand electrical fields provided by pole pieces 48 and plates 50. The ionstream passes through aperature 52 and through mesh 56 on which anacceleration or deceleration potential with respect to the ion has beenplaced. The intensity of the accelerated ion stream is, of course,roughly controlled by the nature of the potential appearing at therespective one of the mesh electrodes 36, 38, or 40 and is finecontrolled by the potential appearing at grid 60. A small sensor grid107 picks up a signal proportional to the ion beam intensity which canbe fed back to control means 96 along lead 109 to provide a feedbacksignal for adjusting the fine control potential as desired. Theintensity of the ion stream, of course, determines, at least in part,the deposition rate of the ionized material on chip 118. but the beamshould be of comparatively low energy so as to prevent deep penetrationof the ions into the chip or undue heating of the latter as well asexecessive sputtering. While this may make good focus somewhat moredifficult to obtain, it is not a serious problem as the resolutionobtainable is still excellent. Typically micron size spots can be hadwith ion currents of the order to l A. If more than simply deposition isdesired, the energy of the ion stream can be controlled to yield somepenetration, for example, to provide localized doping of semiconductorlayers to a given depth, or to provide electrical contacts through acontinuous layer of insulation. The intensity controlled ion stream isnow focussed by disks 64 and 66. Depending upon the configuration of thedisks the beam can be focused to a small circular spot or to anelongated ellipse as desired, depending upon the positions and thepattern which the beam is to lay down. Of course, the nature of thefocus provided by disks 64 and 66 is under the control of focus controlmeans 86 so that changes in focus can be achieved very rapidly andautomatically depending upon the potential the disks have imposedthereon. Inasmuch as the potentials required for focus must be varied toaccommodate for changes in beam energy, means are provided to adjust thefocus control according to the potential on plates 50. Hence, the latterare connected to the focus control means by lead 120.

The now focused beam is moved laterally in direction and at speedsdetermined by variation in the potential on the plates of sets 72 and 74as controlled by scan control means 88 in accordance with signals fromprogrammed controlled device 90. The focused beam striking chip 118,deposits the ions on the latter, Where they discharge and rapidly buildup to form a layer of the material. Lateral deflection of the beamallows this layer to be laid down continuously as a strip, the width ofwhich is determined by the cross-section of the beam. The tendency for astatic charge to build up adjacent chip 118 due to ion discharge isreduced by the ionizing or neutralizing radiation provided by element104.

The various operating parameters, of course, depend on the nature of thedevice being formed by the invention, and are largely under the controlof the various control means. Typically, a number of the criteria uponwhich controls are based, and on the basis of which a program canreadily be established either manually or by computer, are set forth inthe following discussion.

Obviously, the larger the beam deflection rate becomes, the thinner thedeposits produced and vice-versa.

To achieve maximum production in minimum time, one should select thehighest posisble deposition rate and the lowest possible size of theelement being formed. Generally, the deposition rate is proportional tothe beam current which is in turn limited by the maximum power densitywhich chip 118 will stand and the maximum space charge density that canbe compensated by the focus system. Both of these latter parametersdecrease as the focal spot size is decreased; thus for maximumproduction speed the spot size should always be the largest one allowedby the actual component being laid down or written. Deposition speed canbe increased by making the spot elliptical, which increases the maximumallowable current for given allowable heating effects and space charge.

For a given temperature maximum to which the chip can be brought, theallowable beam power increases as the spot size. If the spot size isincreased, however, the current power increases as the square of thespot size and therefore spot size should be limited to only one valuefor each accelerating voltage and ion weight for a given substrate andfocus system. For example, assuming a 5;; spot, and a substrate of highthermal conductivity beryllia, a total beam power of 0.5 watt wouldresult in a temperature rise of about 107 C. Admissible temperatureincreases are limited to a few hundred degrees, thus placing a limit onthe maximum power density. This is somewhat higher when the beam isbeing deflected, which spreads out the heating eifect. Of course, highertemperature increases are possible if block is cooled below ambienttemperature.

One can calculate the amount of current that space charge limits willallow. For example, if one assumes a 5; spot and assumes the tolerablepower is 0.5 watt as the result of a kev. beam with a current of S a.and composed of Al+ ions, one finds a space charge potential of about 15-kv., corresponring to a feasible beam halfangle of 0.15 radian. Thesevalues correspond to a deposition speed of about 265,000 A./ sec. andare enormous in comparison with the present speeds in thermalevaporation techniques. The stated deposition rate corresponds to about0.272 W d mpg/sec. where W,,,, is the atomic weight for a singly chargedion, and g. is the weight in grams. Typically, for aluminum this amountsto 530 /sec. if expressed in volume. While this appears small, it is inactuality an adequate quantity in view of the degree of miniaturizationof the devices which the invention is capable of producing.

Exemplary volume deposition rates in a /sec. for a variety of otherelemental materials are as follows:

C 420 Ni 230 Li 2110 Eu 240 Be 940 Zn 310 B 390 Ge 430 Na 1340 Ga 380 Mg730 As 410 Si 600 Se 560 S 740 Ag 270 K 1930 Sn 410 Ca 1110 Sb 470 Ti420 Te 470 Cr 270 Cs 1670 Mn 280 Ba 910 Fe 260 Ta 220 C0 230 W 190 Au200 Pb 350 Mixed compounds also can be deposited by cycling two or moreion streams at a suflicient repetition rate so that layers of solidmaterial, typically of 10 A. thickness are sucessively laid down. Thus,for example, a BeO strip can be produced by successively depositing verythin films of Be and each in turn being bombarded with a slight excessof 0 ions before the next layer of Be is deposited. Thus, neglecting thevery minute switching time involved in changing the nature of the ionbeam, typical volume deposition rates in p. /sec. for mixed materials orcompounds are as follows:

BeO 290 ZnS 470 MgO 320 GaAs 430 A1 0 280 SiO 540 TiO SiO 460 A numberof unconventional components can readily be produced with the invention.For example, in integrated or thin film circuits it is diflicult toproduce really large capacitors, as multiple layer capacitors requiretoo many fabrication steps and single layer ones will requireunacceptably large lateral dimensions. The first limitation does notapply to the present invention. Typically, thin alternate layers ofconductor and insulators can be very easily deposited on top of oneanother, with a speed limited only by the heating of the substrate.Another factor which will decrease the area required for a givencapacitor is that some of the best dielectric materials, such as thetitanates, can be used here without the unacceptable charge leakage rateproduced in the thermally deposited material as a result of chemicalchanges during exaporation. The latter are prevented here by thedeposition of excess oxygen. Typical capacitors will then consist of anumber of dielectric layers, as thin as may be allowed by tunnellingphenomena (typically several hundred angstroms), separated by thin metallayers.

The conductive layers can typically be formed of deposited aluminumbecause of its chemical resistivity and because outside layers can beeasily insulated by bombardment with oxygen ions. Silver can also beused for conductive layers because of its high conductivity; to provideinsulation of outside surface layers, the silver can be treated withsulfur ions. Calcium will also serve well as aconductor but it must bewell protected at least on outside layers, typically with a surfacelayer of aluminum or aluminum oxide. An added advantage of calciumlayers in capacitors is that if it partly reacts with a Ti insulatinglayer, the reaction product, CaTiO is of even higher dielectricconstant.

Typically, a calcium-calcium titanate capacitor can be made to thefollowing specifications: assume that the capacitor has a 5 x 50elliptical shape with layers, the Ca conductive layers being 100 A.thick and the dielectric layers of TiO being 250 A. thick between the Calayers and on the top and bottom of the capacitor. This can be producedin less than about 30 msec. Such a capacitor would have a seriesinternal resistance of about 1 Q and a capacitance of about 1770 pH.

Attempts to produce printed circuit inductors by thermal vapordeposition techniques have not been very successful as the highestinductances obtained are about 1 9H, and they have Qs below 20. The mainreasons of this is that one cannot readily produce the most efficientshape, Le. a coil, which requires two steps or mask changes for eachturn of the coil and near perfect registrationof successive masksbetween turns.

In the present invention these problems are not serious inasmuch aschanges between steps are very quick and registration is much simpler inthat no mask is required. In order to take advantage of the increase indeposition speed produced by an elliptical spot, a substantially squarecoil shape is preferred. The procedure involves depositing fourelliptical spots of conductor with tips in contact to form a square andthen overcoating all but one tip with an insulator. The next turn of thecoil is started by depositing a fifth spot on top of the spot having theuncoated tip, and so on for as many turns as are desired.

Typically, such a coil is made using aluminum as a conductor and formingthe insulating layers from beams of aluminum and of an excess of oxygenions cycled at a rate sufiicient to insure that the aluminum is fullyoxidized after deposition. This method requires but two ion sources. Ifdesired, another ion beam can be used to deposit a central core offerrite material to increase the inductance. An exemplary coil formed ofAl-Al O used a spot which has an ellipticity of 10 and a minor diameterof about 100 This can be used to form a coil 1 mm. on each side width,for example, 200 turns of 500 A. thick aluminum to provide an inductanceof about 96 ,uH, having .a Q of about 30 at 200 MHz. This coil can beproduced in less than 1 sec.

Better results can be obtained using a three ion-source system toprovide conductive layers of Ag and insulators of BeO. Because thehigher thermal resistance and conductivity of the system allows anincrease of the thermal load, a similar coil can be produced in lessthan 0.3 sec. with a o of about 50 at 200 MHz.

The presence of electron source 110 and collector 114 gives theinvention even more flexibility. Essentially, then the device can beused alternatively as an electron scanning microscope. At any stage ofwriting, the ion beams are shut off, as by biasing electrodes 36, 38,and 40 and the electron source 110 turned on. The resulting electronbeam is focused onto the surface of chip 118 and scanned across thewritten or deposited material. The potential ditference between adjacentareas of the deposited material and substrate alter the intensity of thesecondary electrons emitted or the primary electrons reflected, and isthen detected by collector 114, creating a signal train that can, ifdesired, be converted in the usual manner into an image on a cathode raytube screen. Preferably, this signal train is fed back through lead 116to program controlled device where the latter is computer controlled inorder to adjust any program being computed to accord with theobservations being made by the electron beam.

The attributes of the present invention make it particularly adapted foryet other unique applications. Because it can produce miniaturecomponents with an extremely high packing density, it can be used toproduce very compact electronic memories and indeed, the electron beamaspect of the device can be used to read-out the memory whilst the ionbeams can be used not only to write-in memory of elements but to erasethem as by coating selected memory elements with an insulating layer.The device can also be used to produce very fine optical gratings andreticles, not only at much higher speed than can presently be achievedwith ruling engines but of many materials that cannot readily bemachined.

Since certain changes may be made in the above apparatus and processeswithout departing from the scope of the invention herein involved it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted in an illustrative and notin a limiting sense.

What is claimed is:

1. Method of forming a microelement of a given configuration on a workpiece, comprising the steps of substantially simultaneously producing aplurality of ion beams each of different deposition materials and eachbeam being directed along an individual path substantially in a vacuum;

directing each of said beams along its individual path to apredetermined common path in said vacuum; controlling said beams so thatonly one of said beams at a time can traverse said common path;electrostatically focusing any beam traversing said common path ontosaid work piece; deflecting laterally in two dimensions any beam.traversing said common path so as to trace out a predetermined pathacross said work piece; and

discharging the charge on ions of any beam incident on said work pieceso as to deposit said material along said predetermined path. 2. Methodas defined in claim 1 wherein said beam is electrostatically focused toan elliptical spot onto said work piece.

3. Method of forming a reactance on a substrate and comprising the stepsof:

substantially simultaneously producing in vacuum a plurality of beams ofions each directed along an individual path, the ions of at least afirst of said beams being of normally electrically conductive material,the ions of at least a second of said beams being of material capable offorming an insulating material upon bombardment of a layer of materialfrom which the ions of one of said beams is formed;

directing said beams, only one at a time according to a given sequence,through a common fixed path;

focussing said beams in said sequence onto said substrate;

deflecting each of said beams laterally across said substrate along apredetermined path covering a given area and discharging the ions ofsaid beams so that said ions deposit onto said substrate; and

alternating said beams so that a sandwich of successive layers ofconductive and insulating material are deposited on said substrate.

4. Method as defined in claim 3 wherein said plurality of beams includesonly a beam of ions of said conductive material and a beam of ions ofsaid material capable of forming an insulating material.

5. Method as defined in claim 3 wherein said plurality of beams includesat least three beams, the ions of two of which are of difierent normallyelectrically conductive materials.

6. Method as defined in claim 3 wherein said successive conductivelayers are electrically insulated from one another, so as to form acapacitor.

7. Method as defined in claim 3 wherein adjacent ones of said successiveconductive layers are in electrical con tact with one another at minorportions staggered from layer to layer so as to form an inductive coil.

References Cited UNITED STATES PATENTS 3,294,583 12/ 1966FedoWs-Fedotowsky 3,458,368 7/1969 Haberecht 1!17--2l2 X 3,205,0879/1965 Allen 1l7-93.3 X 3,573,098 3/1971 Bieber et al 1l72l2 ALFRED L.LEAVITI, Primary Examiner K. P. GLYNN, Assistant Examiner U.S. Cl. X.R.11793.3; 215

